A known valve mechanism disclosed, for instance, by Japanese Patent JP-A-2003-239712 uses a rocker arm having a rocker roller to drive a valve disc. In this conventional valve mechanism, the rocker arm has a bearing section at one of its ends and is in contact with the valve disc at the other end. The rocker roller is positioned between these two ends.
A lash adjuster has a pivot at its leading end. The pivot is pivotally supported by a bearing of the rocker arm. When the rocker roller is pressed, the configuration described above causes the rocker arm to turn on the pivot, thereby pushing the valve disc in a valve opening direction. Therefore, when the rocker roller periodically swings, the valve disc can be periodically opened/closed.
In the conventional valve mechanism described above, a variable valve mechanism is positioned over the rocker roller. The variable valve mechanism includes a swing arm, which is in contact with the rocker roller, and a conversion mechanism, which is positioned between the swing arm and a camshaft. The conversion mechanism is capable of converting the rotary motion of the camshaft to a swinging motion of the swing arm and changing a basic posture of the swing arm in accordance with external instructions.
When the basic posture of the swing arm changes, a change occurs in the swing angle between the swing start position at which swing arm operation is started and the pressure start position at which the swing arm starts to push the rocker roller. When the swing angle changes, a maximum displacement amount of the rocker roller changes, as a result, a maximum lift amount of the valve disc changes. In this manner, the conventional valve mechanism described above can change the maximum lift amount of the valve disc.
With regard to the present invention, the applicant is aware of the following document as a related art.    [Patent Document 1] Japanese Patent JP-A-2003-239712